Dog watch

Two half watches of two hours each into which the period from 4 pm to 8 pm is divided. The purpose of dividing this watch into two parts is to produce an uneven number of watches in 24 hours, 7 instead of 6. This ensures that watchkeepers in ships, whether organized into two or three watches, do not keep the same watches every day. These two watches are known as the First Dog and Last Dog.